The Pan-STARRS project has begun a unique program of observing three quarters of the night sky: the systematic search for astronomical objects that change over time. Its data will enable astronomers to search for dangerous asteroids on a possible collision course with Earth, but also to tackle some of astronomy's deepest mysteries: Dark Matter and Dark Energy. Scientists of the Max Planck Institutes for Astronomy and for Extraterrestrial Physics are involved in a number of the survey's key projects, including searches for extra-solar planets, for "failed stars" known as Brown Dwarfs, and for distant active galaxies.

The timeless configuration of stars in the night sky is a veritable symbol of changelessness. Yet closer inspection reveals that there is action in the sky - from objects such as variable stars to rare events such as stellar explosions which are visible for a brief period of time only. A new survey specifically targets such celestial change: Pan-STARRS1 will make repeated observations that should cover all regions within 75% of the night sky at least 30 times, while regions of special interest will be observed several hundred times. The result is a unique "movie of the sky".

"Every month, Pan-STARRS1 will observe one sixth of the sky at five different wavelengths" explains Dr. Roberto Saglia of the Max Planck Institute for Extraterrestrial Physics. "In this way, we can track changes in brightness. We can also use our data for an especially deep look into certain regions of the sky." These regions are observed every night. The resulting data will also be used to draw a particularly detailed three-dimensional map of the Milky Way Galaxy, our cosmic home, and to produce a complete inventory of variable astronomical objects for our cosmic neighbour, the Andromeda galaxy.

Pan-STARRS1 also acts as a classical survey, where astronomers look for known types of celestial objects. It will search, among other things, for extremely faint and red objects, such as Brown Dwarfs (objects that do not have sufficient mass to evolve into proper stars) and the earliest active galaxies ("quasars at redshift z = 7") at distances of more than 13 billion light-years. Another part of the search has a very practical goal: Pan-STARRS1 is set to chart asteroids that could potentially collide with Earth in a catastrophic "global impact" event.

Pan-STARRS' repeated observations of large regions of the sky make it the ideal tool to track phenomena that change over time. A key example are "transiting exoplanets" - planets around distant stars that, as seen from Earth, periodically move in front of their mother star, obscuring a tiny fraction of the star's light and thus causing a slight dip in its apparent brightness. Its observational strategy also increases the chances of Pan-STARRS1 to observe very rare, ephemeral phenomena. An example: With luck, the survey could catch a distant galaxy's central black hole in the act of swallowing a star - an event that leads to an increase in brightness that lasts only a few days. In addition, Pan-STARRS1 astronomers brace for the unexpected. "Whenever astronomers have tried out a new way of looking at the sky, they've been in for surprises," says Prof. Dr. Hans-Walter Rix of the Max Planck Institute for Astronomy. "Pan-STARRS1 is the first systematic, large-scale survey of time-dependent phenomena in the night sky. If history is any guide, we are bound to find something completely new."

Conceived and designed at the University of Hawaii Institute for Astronomy (IfA), the Pan-STARRS1 observatory sits atop the dormant volcano Haleakala but is operated remotely from the Advanced Technology Research Center in Pukalani, Maui. The telescope currently in operation, PanSTARRS1 (PS1) is the prototype whose operation is meant to lead to a larger, more complete survey involving four telescopes of the same type. "PS1 has been taking science-quality data for six months, but now we are doing it dusk-to-dawn every night," says Dr. Nick Kaiser, the IfA scientist who is the principal investigator of the Pan-STARRS project. This marks the transition from the telescope's commissioning and testing phase to science operations.

With a 1.8-meter primary mirror, the PS1 telescope is modest in size - at least by the standards of modern professional astronomy. But PS1 has unique properties, namely an extraordinary field of view more than thirty times the size of the full moon. Mounted on the back of the telescope is the 1.4-Gigapixel camera (which is about the size of a telephone booth) that makes PS1 the world's most powerful survey telescope.

Now that the PS1 telescope has started to take data, the observatory will produce several Petabytes of data over the next years, enough to fill on the order of 1000 DVDs every night. To master this relentless stream of data, a new Pan-STARRS1 computer cluster was built at the Garching computer centre. With 150 TB of storage space on hard disc for rapid data reduction and analysis, long-term storage on magnetic tapes, and 700 CPUs, this new cluster is hard at work churning through the first Pan-STARRS1 survey data. The analysis employs custom-made software that enables astronomers to automate the first steps in the classification of the astronomical objects observed, providing automatic measurements of key properties such as the temperature and metallicity of stars, or the redshift of distant objects.